Stent for positioning in a body conduit or method for producing this stent

ABSTRACT

By a contrast means contained in an inventive stent which has a greater permeability for x-radiation features than the body tissue surrounding the stent in a relevant body conduit, this stent can be clearly detected in its position on an x-ray image of the relevant body conduit while at the same time exhibiting good biological compatibility; a gas, especially one contained in cavities of the stent is provided as a contrast means. The inventive production method for this stent with the aid of a catheter embodied specially for the purpose enables the production of the stent from a malleable polymer mass in the relevant body conduit so that the stent is adapted especially precisely to the shape of the relevant body conduit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German application No. 10 2005 024625.7 filed May 30, 2005, which is incorporated by reference herein inits entirety.

FIELD OF THE INVENTION

The invention relates to a stent for positioning in a body conduit or toa method for producing this stent, with the stent containing a contrastmeans for x-radiation.

BACKGROUND OF THE INVENTION

A stent is a tubular implant which provides radial outwards support forthe wall of a body conduit, e.g. a blood vessel, bile duct, an airconduit or an esophagus. The stent usually consists of the elasticmaterial, e.g. a metal or metal alloy or a polymer, and frequently has amesh or network or spiral-type structure, with stents in the form of ametal mesh being the most widely used. The stent is introduced into therelevant body conduit with the aid of a catheter and is bought intoadhesive contact there with the wall of the body conduit. With bloodvessels specifically stents are introduced into the wall of the vesselas endoluminal vessel prostheses for therapy of stenoses caused byarterosclerotic plaque.

A stent is known from US 2004/0148014 A1 in which markers impermeable tox-rays are distributed, in order to make the position of the stentclearly visible on an x-ray image once it has been used in the relevantbody conduit. These markers most contain substances such as heavy metalsor iodine compounds which, when used in the body conduit—even with anappropriate encapsulation—present a potential danger to health.

SUMMARY OF THE INVENTION

The object of the present invention is to specify a stent which issimple to produce, which, despite being easily visible on an x-rayimage, still exhibits good biological compatibility without a potentialdanger to health.

This object is achieved by a stent or by a method in accordance with theindependent claims; advantageous embodiments of the invention are thesubject of the assigned subclaims in each case.

Through the inventive contrast means contained in the stent, which has agreater permeability for x-radiation than body tissue surrounding thestent in the relevant body conduit, the introduction of a potentiallyhazardous contrast means with a lower permeability for x-radiation inthe body conduit is avoided and yet easy identification of the stentintroduced into the relevant body conduit on an x-ray image of the bodyconduit is still guaranteed.

Contrast means with a higher permeability for x-radiation than thesurrounding body tissue in each case are known as negative contrastmeans; they are shown as dark areas on an x-ray image. On the other handa contrast means with a lower permeability for x-radiation than the bodytissue surrounding it is referred to as a positive contrast means; theyare shown as light areas on the x-ray image. Unlike positive contrastmeans, which as a result of the compounds that they contain, withelements with a high atomic number, are at least potentially damaging tohealth, negative contrast means mostly have good biologicalcompatibility.

A negative contrast means in the form of a gas, especially in the formof carbon dioxide, enables an especially high permeability forx-radiation and thus an especially good detectability of the position ofthe stent in the body conduit on the X-ray image. As a rule gasesexhibit a far lower atomic density than a solid or a liquid with thesame substance so that gases of the low atomic density are accordinglyparticularly permeable for x-radiation. In addition gases, especiallycarbon dioxide, are inexpensive by comparison with the usual positivecontrast means.

By enclosing the gas in cavities of the stent on the one hand thestability of the stent is increased and on the other hand by selectingan appropriate distribution density of the cavities and/or through theform of the hollow cavities the elastic properties of the stent can beadapted to the relevant purpose for which it is used or to the relevantbody conduit; tubular cavities extending in the longitudinal directionof the stent for example allow the stent to be bent easily in thelongitudinal direction without this process reducing the radialstability of the stent. In addition the stent is then also still able tobe detected on the x-ray image if for example a few cavities are notgas-tight and some of the gas escapes when the stent is positioned,during its expansion or during its time in the body conduit. In additiona stent with cavities containing the gas is simple and cheap to produce.

A stent consisting at least partly of a polymer guarantees especiallygood biocompatible properties and a low-cost production of the stent;the stent can for example consist entirely of the polymer or be coatedwith the polymer. A stent made entirely of polymer, such as silicone orrubber for example, where necessary except for the negative contrastmeans, is in addition especially elastic and can also be easily adaptedto a distortion of the body conduit.

In accordance with one embodiment of invention the polymer is embodiedin the form of a polymer foam containing the cavities; a stentconsisting of this polymer foam is especially simple to produce byfoaming up the polymer with the gas. Polyurethane is suitable forexample as the polymer and can be foamed up in a manner known per-sewith little effort. The still liquid polymer can be foamed up in theproduction of the stent both by introducing the gas into it and byletting a gas dissolved in the polymer escape.

In accordance with a further embodiment of the invention the polymer isembodied in the form of small polymer balls containing the cavities;these can be incorporated into the stent particularly easily, e.g. bymixing the polymer balls with a liquid material from which the stent isformed, in which case the liquid material itself can again also be apolymer.

The inventive method of production for the stent consisting at leastpartly of the polymer with simultaneous positioning of this stent in thebody conduit using a catheter positioned in the body conduit with afilling area at least partly enclosing this catheter which can be filledwith a polymer mass to be hardened into a stent provides a simple meansof producing the stent which is clearly visible on the x-ray image andyet is still biologically compatible; in addition the stent is preciselyadapted to the form of the relevant body conduit by been formed in thebody conduit so that the stent is secured against slippage in the bodyconduit and damage to the body conduit by the stent is avoided.

In accordance with an embodiment of the invention there is advantageousprovision for filling the filling area positioned at the positionintended for the stent with a polymer mass temporally accommodated in aninner chamber of the catheter; in this way, especially for simpleintroduction of the catheter into the body conduit, it is possible tofill the filling area with the plastic mass only once the positionintended for the stent is reached.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, as well as further advantageous embodiments of theinvention in accordance with features of the subclaims, are explained ingreater detail below with reference to schematic diagrams of exemplaryembodiments in the drawing, without this restricting the invention tothis exemplary embodiment in any way; The Figures show:

FIG. 1 in a perspective view, a stent divided into two parts made of apolymer, with a contrast means in the form of a gas enclosed incavities;

FIG. 2 a stent as shown in FIG. 1 made of a polymer foamed up with thegas;

FIG. 3 a stent as shown in FIG. 1 with the small polymer ballscontaining the gas;

FIG. 4 in a longitudinal cross-section, a catheter introduced into thebody conduit with a filling area which is enclosed by an envelope andable to be filled with a polymer mass which is held in a capsulearranged in a catheter;

FIG. 5 the catheter shown in FIG. 4 with the filling area being filledwith the polymer mass and thereby expanded towards the wall of the bodyconduit;

FIG. 6 the catheter shown in FIG. 4 with the filling openings from thecapsule to the filling area closed and the envelope separated from thecatheter;

FIG. 7 the body conduit shown in FIG. 4-6 with the stent produced by thecatheter;

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows in a perspective view, a stent made of a polymer which isshown in a cross section at right angles to the longitudinal directionof the stent, divided into a first part 1 and a second part 2, in orderto make the cavities 3 surrounded by the polymer and filled with a gasvisible in a sectional surface 4 of the first part 1.

There is provision to feed a catheter through an opening 5 passingthrough the stent 1, 2 and to place the stent 1, 2 on the catheter insuch a way that the stent encloses an expandable balloon section of thecatheter in the form of a tube. Subsequently the stent 1, 2 isintroduced with the aid of the catheter into a body conduit and isadapted there to the internal diameter of the body conduit by anexpansion of the balloon section. Finally the catheter is removed whilethe stent 1, 2 remains in the body conduit and provides radial supportfor this.

The gas contained in the cavities, e.g. carbon dioxide, operates as anegative contrast means so that the position of the stent 1, 2 withinthe body conduit can be detected on an x-ray image of the body conduit.The more gas is enclosed in the ratio by volume to the remaining stentmaterial in the stent 1, 2 the more clearly the image of the stent 1, 2stands out as a dark area against the image of the body tissuesurrounding the stent 1, 2.

So that the stent, after its expansion into its expanded form, retainsthis form even after the catheter has been removed, the stent consistsat least partly of a plastic deformable material which permanentlyassumes its changed shape through a radial expansion. This material canfor example be embodied in the form of a number of rings distributedover the length of the stent 1, 2 and surrounding the opening 5 in eachcase. Alternatively it is also possible to arrange an elasticallydeformable wire mesh within the stent 1, 2 which keeps the stent 1, 2 inthe expanded state after its expansion.

FIG. 2 like FIG. 1, shows a stent 1, 2 made of polymer, with the polymerbeing embodied in the form of a polymer foam which can be seen from thecross-sectional surface 4. The negative contrast means in the form of agas is enclosed in the cavities 3 of the polymer foam.

FIG. 3 like FIGS. 1 and 2, shows a stent 1, 2 made of polymer, with thepolymer being embodied in the form of small polymer balls 6 which can beseen from the cross-sectional surface 4. The negative contrast means isenclosed in gaseous form in the cavities of the polymer foam. The otherstent material surrounding the small polymer balls in the stent 1, 2 canbe both the same polymer and also another substance, such as a secondpolymer for example.

Instead of a surface enclosed in a radial direction, the stent 1, 2 canalso have a surface in the form of a mesh or in the form of a grid.

FIGS. 4-7 illustrate typical examples based on an exemplary embodimentfor the inventive method for producing a stent 20 by means of a catheter8 with simultaneous positioning of the stent 20 in a body conduit 7.

FIG. 4 shows in a longitudinal cross section a catheter 8 introducedinto a body conduit 7 with an essentially tubular filling area 9surrounding the catheter 8 which is enclosed by an envelope 10 and whichis connected via two filling openings 11 or 12 to an inner chamber inthe form of a cylindrical capsule 14 arranged in the catheter,containing a liquefied and hardenable polymer mass 13. The envelope 10is held onto the catheter at its front and rear end by an extendable andretractable clamping ring 15 or 16 which encloses the entirecircumference of the catheter 8 in each case, so that the filling area 9is completely sealed off from the body conduit 7. The two fillingopenings 11 and 12 each have an opening slider 17 or 18, with which thefilling openings 11 or 12 respectively are closed off. To fill thefilling area 9 with the polymer mass 13 from the capsule 14, a piston 19which can be pushed within the capsule 14 is provided. The clampingrings 15 or 16, the opening sliders 17 or 18 and also the piston 19 areremotely operated automatically or at least partly with the involvementof an operator of the catheter 8. The catheter 8 is already positionedwith its filling area 9 at the position intended for the stent.

In an especially uncomplicated manner the polymer mass 13 is mixed withthe negative contrast means before the filling area 9 is filled withthis polymer mass 13; this removes the need for separate filling of thefilling area 9 with the polymer mass 13 on the one hand and the negativecontrast means 6 on the other hand. In this exemplary embodiment thenegative contrast means in the form of the small polymer balls 6 filledwith carbon-dioxide is mixed in homogeneously with the polymer mass 13before the catheter 8 is introduced into the body conduit 7.

Depending on the contrast means used in each case it is also possible tohave the filling area 9 filled with the negative contrast means beforeit is filled with the polymer mass 13.

When a contrast means in the form of a gas, especially in the form ofcarbon dioxide is used, this is distributed especially easily andcost-effectively by foaming up the polymer mass with the gas in thestent 8. The foaming-up of the gas can be undertaken both before andalso after the filling of the filling area with the polymer mass 13. Inthe case of foaming up in the form of letting the gas escape into thepolymer, this process is expediently undertaken in the filling area 9.

FIG. 5 shows the catheter 8 shown in FIG. 4 with on the one hand thefilling openings 11 and 12 opened by moving one of the opening sliders17 or 18 and on the other hand the piston 19 pushed into the capsule 14,so that the filling area is filled with the polymer mass 13 from thecapsule 14. Filling the filling area with the polymer mass 13 expandsthe filling area so that this advantageously adapts its form and itssize to the body conduit 7. In this case the expansion does not createany undesired expansion forces since the liquefied polymer mass 13 candistribute itself to match the wall of the body conduit 7.

After the filling openings 11 or 12 have been closed again the polymermass 13 is hardened to create the stent 20, depending on the polymer forexample, simply by a hardening period elapsing.

FIG. 6 shows the catheter 8 shown in FIG. 5, with the filling openings11 or 12 being closed again for an especially simple removal of thecatheter 8 from the body conduit 7, especially before the hardening ofthe polymer mass 13. In FIG. 6 the polymer mass 13 is already hardenedinto the stent 20 and in addition the envelope 11 is released from acatheter 8 by retraction of the clamping rings 15 or 16. In this stateit is possible to withdraw the catheter 8 from the body conduit 7 withthe stent 20 simultaneously remaining in the body conduit 7.

To adapt the stent 20 in respect of its internal diameter an inflatableballoon section surrounded by the filling area (9) is additionallyprovided which is inflated after the positioning of the filling area 9at the position intended for the stent 20.

FIG. 7 shows the body conduit 7 shown in the FIGS. 4-6 with the stent 20produced by the catheter 8 after the removal of the catheter 8 from thebody conduit 7, with the envelope released from a catheter 8 remainingwith the stent 20 in the body conduit 7 as a component of the latter. Byusing a material which can be broken down biologically in the bodyconduit 7 for the envelope, the envelope 10 which is essentially onlyneeded to produce the stent 20 and therefore also its possibly undesiredends, is broken down after a period, which depends on the material usedin each case.

By mixing the negative contrast means into the polymer mass 13 the stent20 produced from this polymer mass 13 is easy to detect on an x-rayimage of the body conduit 7.

In an advantageous manner a means for liquefying and/or for hardening ofthe polymer mass 13 by a change of temperature is provided; this enablesthe polymer mass 13, because of its good deformability in the liquidstate, to be particularly well adapted to the properties of the bodyconduit 7 and enables the filling area 9 to be filled especially simply.It is possible for liquefying and/or hardening of the polymer mass 13 byheating it up, to arrange a heating element in the catheter 8.

To enable stents of different lengths to be produced with the samecatheter, further clamping rings can be provided between the clampingrings 15 or 16. The envelope 10 is accordingly held by one of its endswith clamping ring 16 and with its other end by one of the otherclamping rings.

The invention can be summarized as follows: Through a contrast meanscontained in an inventive stent which exhibits a higher permeability forx-radiation than body tissue surrounding the stent in a relevant bodyconduit, this stent can be clearly detected in its position on the x-rayimage of the relevant body conduit and at the same time has goodbiological compatibility; A gas contained in a cavities of the stent isin particular provided as the contrast means. The inventive productionmethod for this stent with the aid of a catheter embodied especially forthe purpose enables the production of the stent from a malleable polymermass in the relevant body conduit so that the stent is adaptedespecially precisely to the shape of the relevant body conduit.

1-15. (canceled)
 16. A stent arranged in a body conduit of a patient,comprising: a plastic deformable material that forms the stent; and acontrast medium that contains in the stent with a higher permeabilityfor an x-radiation than body tissues surrounding the stent and makes thestent to be easily visible in an x-ray image without a potential dangerto healthy of the patient.
 17. The stent as claimed in claim 16, whereinthe contrast medium is a gas.
 18. The stent as claimed in claim 17,wherein the gas is carbon dioxide.
 19. The stent as claimed in claim 17,wherein the stent has cavities in which the gas is enclosed.
 20. Thestent as claimed in claim 16, wherein the stent comprises a polymermaterial.
 21. The stent as claimed in claim 20, wherein the polymermaterial is a polymer foam.
 22. The stent as claimed in claim 16,wherein the plastic deformable material permanently maintains a shapechange through a radial expansion of the stent when the stent is in thebody conduit.
 23. A method for forming a stent in a body conduit of apatient, comprising: positioning a catheter at a position of the bodyconduit where the stent is intended to be placed; arranging an tubularfilling area surrounding a part of the catheter; filling the tubularfilling area with a hardenable polymer mass; hardening the polymer massin the tubular filling area to form the stent; and removing the catheterfrom the body conduit with the stent remaining in the body conduit. 24.The method as claimed in claim 23, wherein a contrast medium is mixedwith the polymer mass or brought into the filling area before thefilling.
 25. The method as claimed in claim 24, wherein the contrastmedium has a higher permeability for an x-radiation than body tissuessurrounding the stent which makes the stent to be easily visible in anx-ray image.
 26. The method as claimed in claim 24, wherein the contrastmedium is a gas and distributed by foaming up the polymer mass with thegas in the stent.
 27. The method as claimed in claim 26, wherein the gasis a carbon dioxide.
 28. The method as claimed in claim 23, wherein thefilling area is expandable by filling with the hardenable polymer mass.29. The method as claimed in claim 23, wherein the filling area isaccommodated in an inner chamber of the catheter.
 30. The method asclaimed in claim 29, wherein the inner chamber is a closable capsule.31. The method as claimed in claim 30, wherein an opening from the innerchamber to the filling area is closed off after the filling and beforethe removal of the catheter from the body conduit.
 32. The method asclaimed in claim 31, wherein the opening from the inner chamber to thefilling area is closed off after the filling and before the hardening ofthe polymer mass.
 33. The method as claimed in claim 23, wherein thepolymer mass is liquefied or hardened in the filling area by atemperature change.
 34. The method as claimed in claim 23, wherein aballoon section of the catheter surrounded by the filling area isinflated after positioning the catheter in the body conduit.